1. Field of the Invention
The present invention involves a tactile designation device for capacitance detection, and particularly, a device comprising a glass plate covered by a metallic deposit on at least one part of its surface and supported by flexible strips, means of supply for the metallic surface, and strain gauges that are set on the strips in order to measure flexing of the strips.
2. Background Art
In prior art devices, a conducting metallic deposit is covered by an insulating material on its useful surface which is carried out by processing in thin layers with the deposit of a non-reflecting multicoated layer on the metallic layer, or by means of adhesion of a thin glass with non-reflective processing.
These devices are designed to form transparent tactile keyboards provided with integrated pressure detection means. For example, such a system is set up in front of a liquid crystal display, and allows a particular displayed zone to be designated by tactile means (for example, with a finger).
For this purpose, electric means determine the position of a finger on the metallized plate and detects, due to the strain gauges, a deflection of the plate due to pressure exerted by the finger. These devices thereby provide a touch screen without significantly altering the viewing of images presented on the display and do so at a competitive cost.
The tactile designation devices presently known, however, exhibit a number of disadvantages. A disadvantage of prior art devices is that they require a supporting mechanism for maintaining and guiding the glass plate, as well as mechanical adjustments of the plate's position on each strip in order to be able to compensate for positioning allowance.
Another disadvantage is that the connection links of the metallized surface of the plate as well as the strain gauges must follow the movements of the plate.